A ketomalonic acid diester or a hydrate thereof is a compound useful as a raw material in production of a pyrazin-2-on-3-carboxylic acid ester derivative by reaction with diamine (see Patent Documents 1 to 4, and Non-patent Documents 1 to 2). This reaction is used in production of a medicine or an agricultural chemical, and the like, particularly as a method for producing a quinoxalinone derivative from aromatic diamine.
Conventionally, as a synthesis method of ketomalonic acid diester from malonic acid diester, direct methods and indirect methods were reported. However, none of them has been industrialized due to the toxicity or the difficulty in handling reagents, and the like. As a synthesis method of ketomalonic acid diester from malonic acid diester, known is, for example, a process of producing ketomalonic acid diester by oxidizing malonic acid diester with an oxidant such as selenium dioxide (for example, see Non-patent Document 3 wherein the yield rate is 32.3% of the theoretical yield on the basis of selenium dioxide used), dinitrogen trioxide (for example, see Non-patent Document 4 wherein the yield rate is 74 to 76%) and chromium trioxide (for example, see Non-patent Document 6 wherein the yield rate 70%). However, these methods have problems such as toxicity of reagents, poor safety or operability of reagents, low yield rate, use of a special reactor, or use of a transitional metal.
In addition, there are known methods of producing ketomalonic acid diester as follows: a method of reacting a compound in which the active methylene moiety of malonic acid diester is substituted with bromine, with silver nitrate (for example, see Non-patent Document 7), a method of reacting an azo group-substituted compound with dimethyl dioxirane (for example, see Non-patent Document 8), a method of reacting a methylene group-substituted compound with ozone (for example, see Non-patent Documents 5 and 9), a method of reacting a hydroxy group-substituted compound with a noble metal catalyst (for example, see Patent Document 5) and the like. However, these methods have drawbacks of using tartronic acid which is far more expensive than malonic acid diester, as a raw material, or necessity for previous modification of the active methylene moiety of malonic acid diester, or have economical and operational problems. In addition, these processes have problems such as use of expensive reagents, use of special reacting agents, use of special reactors, use of expensive catalysts, or use of transitional metals.